Here's some links to look at:
1) First, the online Administrative Code for Maryland. I used this database as a starting point. I searched for "Air Gun."
http://www.dsd.state.md.us/COMAR/ComarHome.html 2) Deer and Bear:
http://www.dsd.state.md.us/comar/comarhtml/08/08.03.04.05.htm Here's what is says about deer/bear:
.05 Devices for Hunting Deer and Black Bear.
A. Only the weapons described in §§B and C of this regulation may be used to hunt deer and black bear. All other weapon types are prohibited for hunting deer or black bear....
C. Firearms..... (5) An air gun that:(a) Propels one .40 caliber or greater bullet or ball at a single discharge which generates at least 400 foot-pounds of muzzle energy; or(b) Propels an arrow at least 18” in length with a minimum speed of 300 feet per second at release, uses an arrow with a sharpened broadhead with metal points and a minimum width of 7/8 inch, and has a working safety if the device is fired by a trigger. So the way I take that, the air gun must 1) generate at least 400fpe, 2) must be .40 or greater, and 3) must shoot a bullet or a ball. As where bullets are balls are named, and pellets are not, a pellet wouldn't be legal for a deer even if its .40 and 400fpe.
3) Turkey:
http://www.dsd.state.md.us/comar/comarhtml/08/08.03.04.06.htm 06 Wild Turkey Hunting....
C. During the spring and winter turkey seasons a person may only hunt turkeys with an air gun propelling an arrow, a bow, or shotgun with shotgun shells loaded with shot size number 4 or smaller. D. During the fall turkey season a person may only hunt turkeys with a rifle, handgun, bow, air gun, or shotgun with shotgun shells loaded with:(1) Shot size number 4 or smaller; or(2) A solid single projectile, such as a pumpkin ball, sabot, or slug. So in the Spring, only an air bow may be used. In the Fall, any airgun may be used so long as it shoots a solid projectile. So a pellet would suffice.
4) Furbearers.
http://www.dsd.state.md.us/comar/comarhtml/08/08.03.06.05.htm I didn't reproduce the text, but the regulations present no caliber or projectile restrictions. They just state that air guns are legal for furbearers.
Maryland hunters will need to check with their local LEOs to determine how the rules will be implemented. I am posting this info more to point out that often official state brochures are inaccurate relating to air guns. Look how different the brochure reads from the posted regulations. States often farm these brochures out to third parties or are compiled by state employees who may themselves not have an accurate grasp of the regulations. When you have a conversation with your local LEO, be armed with the actual correct regulations. He or she may not be aware of them. Often the LEOs are just consulting a field guide or the same citizens brochure. Respectfully pointing out mistakes in the brochures to the right people make changes happen (but don't have that conversation while he's contemplating writing you up, instead, have that conversation in advance before you go hunting. Ask permission, not forgiveness).
I am a criminal prosecutor in Florida and I regularly have to interpret our State hunting regulations in prosecutions against alleged hunting violations. I cannot speak for Maryland. I have no authority there. But I firmly believe that good conversations I've had with the right people have changed Florida's airgun regulations for the better, as well as changed the official brochures to accurately reflect what has been legal under the regulations for years. Someone is going to need to respectfully point out to Maryland that the brochure and the regulations aren't matching.